This invention relates to corrective appliances and more particularly corrective insoles and to the manufacture of corrective insoles or insole inserts constructed to give effective support and relief of the ailment or infirmity known as shin splints.
Shin splints are located in the lower leg on the medial side of the tibia, in the area of the interosseous membrane, which is between the tibia and fibula. Each time the foot makes contact with the ground, the body must absorb a "load." This load is generally the athlete's own body weight. This loading places strenuous demands upon the foot and leg, including the bones in the feet and leg. If measures can be taken to reduce these stresses, then the shoe or an appropriate insole has functioned properly and potential injury can be avoided to the lower leg.
Biomechanics evaluate the demands of a particular injury avoidance. Each activity has its own unique movement, and different stresses on the lower extremities. When running, regardless of the runner's foot fall pattern, the foot is angled slightly inward from the vertical (or "supinated" in biomechanical terms) at touchdown, causing an initial landing on the outside or valgus portion, or lateral aspect, of the heel. Impact results in the foot being rapidly forced on the running surface, causing a bending, or flexion, phase in the knee and hip. Further loading upon initial impact causes the bottom of the foot to be turned away from the body's midline--a phase biomechanics call pronation. The ankle is rolled toward the midline and the whole foot is turned out from the body's midline. This causes the ankle to appear to move in toward the center of the body as the foot lands flat on the ground. After reaching maximum pronation, a propulsion phase begins and all the foregoing actions are reversed.
Pronation or inversion, where the bottom of the foot is turned toward the body's midline is described as abnormal. Pronation during walking and running allows the impact forces to be absorbed over a greater time period. Thus, reducing the effective magnitude of the force without pronation causes excessive stress that would exit on the supporting leg structures. Excessive pronation may be injurious to the walker or runner, and is generally associated with complications of the knee, ankle and lower leg, as in the shin splint. Based on knowledge of the foot function during walking or running, it is desirable to protect the foot and lower leg form excessive forces which will cause injury or irritated membrane in the lower leg.
Since shin splints are located in the lower leg on the medial side of the tibia, when the membrane in the area of the interosseous membrane gets irritated, inflamed and very sore, the condition is known as shin splints. This irritation is common to joggers and walkers as an ailment which comes from running or walking on a hard or uneven surface or sometimes just from walking or running on any surface.